Multi-mode audio amplifiers

ABSTRACT

A multimode audio amplifier comprises: a mode controller adapted to provide a control signal; and at least one multimode module, wherein each of the multimode modules has a plurality of operating modes, wherein the operating modes are selected in accordance with the control signal, wherein changing the operating modes results in a measurable change in at least one characteristic of the multimode audio amplifier; wherein the characteristics of the multimode audio amplifier consist of signal to noise ratio (SNR); total harmonic distortion and noise (THD+N); input to output delay; power consumption; and efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/940,223, filed on May 25, 2007 and U.S.Provisional Patent Application Ser. No. 60/952,760, filed Jul. 30, 2007,the disclosures thereof incorporated by reference herein in theirentirety.

BACKGROUND

The present invention relates generally to signal processing. Moreparticularly, the present invention relates to multi-mode audioamplifiers.

SUMMARY

In general, in one aspect, an embodiment features a multimode audioamplifier comprising: a mode controller adapted to provide a controlsignal; and at least one multimode module, wherein each of the multimodemodules has a plurality of operating modes, wherein the operating modesare selected in accordance with the control signal, wherein changing theoperating modes results in a measurable change in at least onecharacteristic of the multimode audio amplifier; wherein thecharacteristics of the multimode audio amplifier consist of signal tonoise ratio (SNR); total harmonic distortion and noise (THD+N); input tooutput delay; power consumption; and efficiency.

Embodiments of the amplifier can include one or more of the followingfeatures. In some embodiments, the at least one multimode moduleincludes at least one of: an equalizer; a sampling module; a noiseshaper; a pulse width modulator; and an analog output module. Someembodiments comprise a portable device comprising the amplifier. Someembodiments comprise a mobile telephone comprising the amplifier. Someembodiments comprise a variable-length finite impulse response (FIR)filter adapted to provide an output signal based on an input signal,wherein a length of the variable-length FIR filter is selected inaccordance with the control signal, wherein the length of thevariable-length FIR filter represents at least one of an order of thevariable-length FIR filter, and a number of taps of the variable-lengthFIR filter.

In general, in one aspect, an embodiment features a multimode audioamplifier comprising: means for providing a control signal; and at leastone multimode module means for operating in a plurality of modes,wherein each of the module means has a plurality of the modes, whereinthe modes are selected in accordance with the control signal, whereinchanging the modes results in a measurable change in at least onecharacteristic of the multimode audio amplifier; wherein thecharacteristics of the multimode audio amplifier consist of signal tonoise ratio (SNR); total harmonic distortion and noise (THD+N); input tooutput delay; power consumption; and efficiency.

Embodiments of the amplifier can include one or more of the followingfeatures. In some embodiments, the at least one multimode module meansincludes at least one of: an equalizer; a sampling module; a noiseshaper; a pulse width modulator; and an analog output module. Someembodiments comprise a portable device comprising the amplifier. Someembodiments comprise a mobile telephone comprising the amplifier. Someembodiments comprise filter means for providing an output signal basedon an input signal, wherein a length of the filter means is selected inaccordance with the control signal, wherein the length of the filtermeans represents at least one of an order of the filter means, and anumber of taps of the filter means.

In general, in one aspect, an embodiment features a method comprising:receiving a control signal; and operating at least one multimode moduleof a multimode audio amplifier in a plurality of modes, wherein each ofthe modules has a plurality of the modes, wherein the modes are selectedin accordance with the control signal, wherein changing the modesresults in a measurable change in at least one characteristic of themultimode audio amplifier; wherein the characteristics of the multimodeaudio amplifier consist of signal to noise ratio (SNR); total harmonicdistortion and noise (THD+N); input to output delay; power consumption;and efficiency.

Embodiments of the method can include one or more of the followingfeatures. In some embodiments, the at least one multimode moduleincludes at least one of: an equalizer; a sampling module; a noiseshaper; a pulse width modulator; and an analog output module. Someembodiments comprise providing a FIR filter; selecting a length of theFIR filter in accordance with the control signal, wherein the length ofthe filter means represents at least one of an order of the FIR filter,and a number of taps of the FIR filter.

In general, in one aspect, an embodiment features a computer programexecutable on a processor, comprising: instructions for receiving acontrol signal; and instructions for operating at least one multimodemodule of a multimode audio amplifier in a plurality of modes, whereineach of the modules has a plurality of the modes, wherein the modes areselected in accordance with the control signal, wherein changing themodes results in a measurable change in at least one characteristic ofthe multimode audio amplifier; wherein the characteristics of themultimode audio amplifier consist of signal to noise ratio (SNR); totalharmonic distortion and noise (THD+N); input to output delay; powerconsumption; and efficiency.

Embodiments of the computer program can include one or more of thefollowing features. In some embodiments, the at least one multimodemodule includes at least one of: an equalizer; a sampling module; anoise shaper; a pulse width modulator; and an analog output module. Someembodiments comprise providing a FIR filter; selecting a length of theFIR filter in accordance with the control signal, wherein the length ofthe filter means represents at least one of an order of the FIR filter,and a number of taps of the FIR filter.

In general, in one aspect, an embodiment features an apparatuscomprising: a filter controller adapted to provide a control signal; anda variable-length finite impulse response (FIR) filter adapted toprovide an output signal based on an input signal, wherein a length ofthe variable-length FIR filter is selected in accordance with thecontrol signal, wherein the length of the variable-length FIR filterrepresents at least one of an order of the variable-length FIR filter,and a number of taps of the variable-length FIR filter.

Embodiments of the apparatus can include one or more of the followingfeatures. In some embodiments, the variable-length FIR filter comprises:a plurality of fixed-length FIR filters, wherein each of thefixed-length FIR filters is adapted to provide a respective filteredsignal based on the input signal, and further wherein each of thefixed-length FIR filters has a different length; and an output moduleadapted to provide one of the filtered signals as the output signal inaccordance with the control signal. In some embodiments, thevariable-length FIR filter comprises: a first fixed-length FIR filteradapted to provide a first filtered signal based on the input signal; asecond fixed-length FIR filter adapted to provide a second filteredsignal based on the first filtered signal; and an output module adaptedto provide one of the first and second filtered signals as the outputsignal in accordance with the control signal. In some embodiments, thefilter controller provides the control signal based on at least one of acharacteristic of the input signal, and a battery level of a batteryproviding power to the variable-length FIR filter. In some embodiments,the characteristic of the input signal comprises at least one of: a typeof the input signal; and a bandwidth of the input signal. In someembodiments, the type of the input signal comprises at least one of:voice; and music. Some embodiments comprise an amplifier comprising theapparatus. Some embodiments comprise at least one multimode module,wherein each of the multimode modules has a plurality of operatingmodes, and wherein the operating modes are selected in accordance withthe control signal. In some embodiments, the at least one multimodemodule includes at least one of: an equalizer; a sampling module; anoise shaper; a pulse width modulator; and an analog output module. Someembodiments comprise a portable device comprising the amplifier. Someembodiments comprise a mobile telephone comprising the amplifier.

In general, in one aspect, an embodiment features an apparatuscomprising: filter controller means for providing a control signal; andfilter means for providing an output signal based on an input signal,wherein a length of the filter means is selected in accordance with thecontrol signal, wherein the length of the filter means represents atleast one of an order of the filter means, and a number of taps of thefilter means.

Embodiments of the apparatus can include one or more of the followingfeatures. In some embodiments, the filter means comprises: a pluralityof filters means for providing a respective filtered signal based on theinput signal, wherein each of the filter means has a different length;and output means for providing one of the filtered signals as the outputsignal in accordance with the control signal. In some embodiments, thefilter means comprises: first filter means for providing a firstfiltered signal based on the input signal; second filter means forproviding a second filtered signal based on the first filtered signal;and output means for providing one of the first and second filteredsignals as the output signal in accordance with the control signal. Insome embodiments, the filter controller means provides the controlsignal based on at least one of a characteristic of the input signal,and a battery level of a battery providing power to the filter means. Insome embodiments, the characteristic of the input signal comprises atleast one of: a type of the input signal; and a bandwidth of the inputsignal. In some embodiments, the type of the input signal comprises atleast one of: voice; and music. Some embodiments comprise an amplifiercomprising the apparatus. Some embodiments comprise at least onemultimode module means for operating in a plurality of modes, whereineach of the module means has a plurality of operating modes, wherein theoperating modes are selected in accordance with the control signal,wherein changing the operating modes results in a measurable change inat least one characteristic of the multimode audio amplifier. In someembodiments, the at least one multimode module means includes at leastone of: means for equalizing; means for sampling; means for shapingnoise; means for pulse width modulating; and means for analogoutputting. Some embodiments comprise a portable device comprising theamplifier. Some embodiments comprise a mobile telephone comprising theamplifier.

In general, in one aspect, an embodiment features a method comprising:receiving a control signal; and providing an output signal based on aninput signal, including filtering the input signal with avariable-length FIR filter, wherein a length of the variable-length FIRfilter is selected in accordance with the control signal, wherein thelength of the variable-length FIR filter represents at least one of anorder of the variable-length FIR filter, and a number of taps of thevariable-length FIR filter.

Embodiments of the method can include one or more of the followingfeatures. In some embodiments, filtering the input signal with thevariable-length FIR filter comprises: providing the input signal to aplurality of fixed-length FIR filters, wherein each of the fixed-lengthFIR filters provides a respective filtered signal based on the inputsignal, wherein each of the fixed-length FIR filters has a differentlength; and providing one of the filtered signals as the output signalin accordance with the control signal. In some embodiments, filteringthe input signal with the variable-length FIR filter comprises:providing the input signal to a first fixed-length FIR filter, whereinthe first fixed-length FIR filter provides a first filtered signal basedon the input signal; providing the first filtered signal to a secondfixed-length FIR filter, wherein the second fixed-length FIR filterprovides a second filtered signal based on the first filtered signal;and providing one of the first and second filtered signals as the outputsignal in accordance with the control signal. Some embodiments compriseproviding the control signal based on at least one of a characteristicof the input signal, and a battery level of a battery providing power tothe variable-length FIR filter. In some embodiments, the characteristicof the input signal comprises at least one of: a type of the inputsignal; and a bandwidth of the input signal. In some embodiments, thetype of the input signal comprises at least one of: voice; and music.Some embodiments comprise providing the control signal to at least onemultimode module, wherein each of the multimode modules has a pluralityof operating modes, and wherein the operating modes are selected inaccordance with the control signal. In some embodiments, the at leastone multimode module includes at least one of: an equalizer; a samplingmodule; a noise shaper; a pulse width modulator; and an analog outputmodule.

In general, in one aspect, an embodiment features a computer programexecutable on a processor, comprising: instructions for receiving acontrol signal; and instructions for providing an output signal based onan input signal, including filtering the input signal with avariable-length FIR filter, wherein a length of the variable-length FIRfilter is selected in accordance with the control signal, wherein thelength of the variable-length FIR filter represents at least one of anorder of the variable-length FIR filter, and a number of taps of thevariable-length FIR filter.

Embodiments of the computer program can include one or more of thefollowing features. In some embodiments, the instructions for filteringthe input signal with the variable-length FIR filter comprises:instructions for providing the input signal to a plurality offixed-length FIR filters, wherein each of the fixed-length FIR filtersprovides a respective filtered signal based on the input signal, whereineach of the fixed-length FIR filters has a different length; andinstructions for providing one of the filtered signals as the outputsignal in accordance with the control signal. In some embodiments, theinstructions for filtering the input signal with the variable-length FIRfilter comprises: instructions for providing the input signal to a firstfixed-length FIR filter, wherein the first fixed-length FIR filterprovides a first filtered signal based on the input signal; instructionsfor providing the first filtered signal to a second fixed-length FIRfilter, wherein the second fixed-length FIR filter provides a secondfiltered signal based on the first filtered signal; and instructions forproviding one of the first and second filtered signals as the outputsignal in accordance with the control signal. Some embodiments compriseinstructions for providing the control signal based on at least one of acharacteristic of the input signal, and a battery level of a batteryproviding power to the variable-length FIR filter. In some embodiments,the characteristic of the input signal comprises at least one of: a typeof the input signal; and a bandwidth of the input signal. In someembodiments, the type of the input signal comprises at least one of:voice; and music. Some embodiments comprise instructions for providingthe control signal to at least one multimode module, wherein each of themultimode modules has a plurality of operating modes, and wherein theoperating modes are selected in accordance with the control signal. Insome embodiments, the at least one multimode module includes at leastone of: an equalizer; a sampling module; a noise shaper; a pulse widthmodulator; and an analog output module.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a class-D amplifier including a variable-length FIR filteraccording to an embodiment of the present invention.

FIG. 2 shows a process for the class-D amplifier of FIG. 1 according toan embodiment of the present invention.

FIG. 3 shows a filter module according to an embodiment of the presentinvention.

FIG. 4 shows a variable-length FIR filter according to an embodiment ofthe present invention.

FIG. 5 shows a variable-length FIR filter including a plurality offixed-length FIR filters connected in series according to an embodimentof the present invention.

FIG. 6 shows a variable-length FIR filter including a plurality offixed-length FIR filters connected in parallel according to anembodiment of the present invention.

FIG. 7 shows a mobile telephone including the class-D amplifier of FIG.5 according to one embodiment.

FIG. 8 shows a process for the mobile telephone of FIG. 7 according toan embodiment of the present invention.

The leading digit(s) or each reference numeral used in thisspecification indicates the number of the drawing in which the referencenumeral first appears.

DETAILED DESCRIPTION

Embodiments of the present invention provide multimode audio amplifiers.Each multimode audio amplifier includes at least one multimode module.Each multimode module has a plurality of operating modes. The operatingmodes are selected in accordance with a control signal. Changingoperating modes results in a measurable change in at least onecharacteristic of the multimode audio amplifier. Those characteristicscan include signal to noise ratio (SNR); total harmonic distortion andnoise (THD+N); input to output delay; power consumption; and efficiency.The control signal can be based on a characteristic of an input signalfor the amplifier, a battery level of a battery providing power to theamplifier, and the like.

Embodiments of the present invention also provide variable-length finiteimpulse response (FIR) filters. The length of the variable-length FIRfilter can be selected in accordance with the control signal provided bya filter controller. The filter controller can provide the controlsignal based on a characteristic of an input signal processed by thevariable-length FIR filter, a battery level of a battery providing powerto the variable-length FIR filter, and the like. The characteristic ofthe input signal can include a type of the input signal, a bandwidth ofthe input signal, and the like. The type of the input signal can includevoice, music, and the like. The variable-length FIR filters can beemployed in the multimode audio amplifiers disclosed herein.

FIG. 1 shows a class-D amplifier 100 according to an embodiment of thepresent invention. Although in the described embodiments, the elementsof class-D amplifier 100 are presented in one arrangement, otherembodiments may feature other arrangements, as will be apparent to oneskilled in the relevant arts based on the disclosure and teachingsprovided herein. For example, the elements of class-D amplifier 100 canbe implemented in hardware, software, or combinations thereof.

Referring to FIG. 1, class-D amplifier 100 includes a first-in first-out(FIFO) buffer 104, a deemphasis module 106, a mute module 108, a volumecontrol module 110, a channel mixer 112, an equalizer 114, an upsampler116, FIR filter 102, a sampling module 118, a noise shaper 120, apulse-width modulator (PWM) 122, an analog output module 124, and acontroller 126. Class-D amplifier 100 can be used to amplify an inputaudio signal 128.

FIG. 2 shows a process 200 for class-D amplifier 100 of FIG. 1 accordingto an embodiment of the present invention. Although in the describedembodiments, the elements of process 200 are presented in onearrangement, other embodiments may feature other arrangements, as willbe apparent to one skilled in the relevant arts based on the disclosureand teachings provided herein. For example, in various embodiments, someor all of the steps of process 200 can be executed in a different order,concurrently, and the like. As another example, while class-D amplifier100 is described in terms of amplifying an input audio signal 128,class-D amplifier 100 can also be used to amplify other sorts ofsignals.

Referring to FIG. 2, FIFO buffer 104 buffers input audio signal 128(step 202). Input audio signal 128 can be analog or digital. Deemphasismodule 106 can be used to improve the signal-to-noise ratio of the audiosignal by decreasing the magnitude of selected frequencies (step 204).Mute module 108 can be used to mute the volume of the audio signal (step206). Volume control module 110 can be used to control the volume of theaudio signal (step 208). Channel mixer 112 can be used to mix the leftand right audio channels of the audio signal, for example when the audiosignal represents voice (step 210). Equalizer 114 can be used toequalize the audio signal (step 212).

Upsampler 116 upsamples the audio signal (step 214). For example,upsampler 116 can implement 2× upsampling by inserting a zero betweeneach pair of samples of the audio signal. FIR filter 102 filters theupsampled signal (step 216). FIR filter 102 can be implemented as alow-pass filter. FIR filter 102 can be implemented as any of thevariable-length FIR filters described below.

Sampling module 118 can be used to resample, natural sample, andspread-spectrum sample the audio signal (step 218). Noise shaper 120 canbe used to shape the noise of the audio signal (step 220). PWM 122 canbe used to pulse-width modulate the audio signal (step 222). Analogoutput module 124 can be used to output the audio signal to a speaker,headphones, and the like (step 224).

Different applications may have different requirements for audioamplifiers. For example, playing MP3 music may require an amplifier witha high signal to noise ratio (SNR) of 100 dB or more, whereas amplifyingthe human voice for telephone conversation requires an SNR of only 80 dBor less. Some devices, such as mobile phones, may be used for both musicplayback and voice conversation. Embodiments disclosed herein provide amultimode amplifier that can satisfy different requirements with asingle amplifier.

In some embodiments, one or more other modules within amplifier 100 canbe implemented as a multimode module having a plurality of operatingmodes which are selected in accordance with control signal 130 providedby controller 126. For example, equalizer 114 can be disabled when audiosignal 128 represents voice, and enabled when audio signal 128represents music. As another example, the precision of sampling module118 can be reduced for low-bandwidth audio signals 128, for example byreducing the frequency of a sampling sawtooth wave employed inspread-spectrum sampling. As another example, the order of a filter usedby noise shaper 120 can be selected according to control signal 130. Asanother example, the bit precision of pulse-width modulator (PWM) 122can be selected according to control signal 130. As another example, thetopology of analog Output module 124 can be selected according tocontrol signal 130. Changing the operating modes of the multimode moduleresults in a measurable change in at least one characteristic ofamplifier 100. Those characteristics can include, for example, signal tonoise ratio (SNR); total harmonic distortion and noise (THD+N); input tooutput delay; power consumption; and efficiency.

In some embodiments, the multimode amplifier includes a variable-lengthFIR filter. FIR filter 102 has a plurality of lengths, which areselected according to a control signal 130 provided by controller 126.Controller 126 can select the length of filter 102 according to abandwidth of audio signal 128. For example, when audio signal 128represents 8 kHz voice, controller 126 can select a relatively shortfilter length, and when audio signal 128 represents 44.1 kHz CD audio,controller 126 can select a relatively long filter length.

FIG. 3 shows a filter module 300 according to an embodiment of thepresent invention. Although in the described embodiments, the elementsof filter module 300 are presented in one arrangement, other embodimentsmay feature other arrangements, as will be apparent to one skilled inthe relevant arts based on the disclosure and teachings provided herein.For example, the elements of filter module 300 can be implemented inhardware, software, or combinations thereof.

Referring to FIG. 3, filter module 300 includes a variable-length FIRfilter 302 and a filter controller 304. Filter controller 304 provides acontrol signal 306. Variable-length FIR filter 302 provides an outputsignal 310 based on an input signal 308. The length of variable-lengthFIR filter 302 is selected in accordance with control signal 306. Thelength of variable-length FIR filter 302 represents the order of thevariable-length FIR filter 302, the number of taps of variable-lengthFIR filter 302, or both.

Filter module 300 can provide control signal 306 based on informationsuch as a characteristic of input signal 308, a battery level of abattery 312 providing power to variable-length FIR filter 302, and thelike. The characteristic of input signal 308 can include a type of inputsignal 308, a bandwidth of input signal 308, and the like. The type ofinput signal 308 can include voice, music, and the like.

FIG. 4 shows a variable-length FIR filter 400 according to an embodimentof the present invention. Although in the described embodiments, theelements of variable-length FIR filter 400 are presented in onearrangement, other embodiments may feature other arrangements, as willbe apparent to one skilled in the relevant arts based on the disclosureand teachings provided herein. For example, the elements ofvariable-length FIR filter 400 can be implemented in hardware, software,or combinations thereof. Variable-length FIR filter 400 can be used toimplement variable-length FIR filter 302 of FIG. 3.

Referring to FIG. 4, variable-length FIR filter 400 includes N delaymodules 402A-N, N summers 404A-N, and N switches 406A-N. Delay module402A receives an input signal 408. Each of the remaining delay modules402B-N receives the output of the previous delay module 402. Each delaymodule 402 delays its input signal by a fixed delay.

In some embodiments, variable-length FIR filter 400 includes Nmultipliers 412A-N. Each multiplier 412 multiplies the output of acorresponding delay module 402 by a respective coefficient C(A N). Eachswitch 406 couples one of summers 404 with the corresponding multiplier412 in accordance with a control signal 414.

Summer 404A receives input signal 408, and outputs the sum of inputsignal 408 and the output of multiplier 412A. Each of the remainingsummers 404B-N outputs the sum of the output of the previous summer 404and the output of the corresponding multiplier 412.

Control signal 414 can be provided by controller 304 of FIG. 3, and canbe implemented as a vector transmitted over a plurality of control lineseach controlling one of switches 406. Control signal 414 changes thelength of variable-length FIR filter 400 by opening or closing one ormore of switches 406, thereby changing the order of filter 400, thenumber of taps of filter 400, or both.

FIG. 5 shows a variable-length FIR filter 500 including a plurality offixed-length FIR filters connected in series according to an embodimentof the present invention. Although in the described embodiments, theelements of variable-length FIR filter 500 are presented in onearrangement, other embodiments may feature other arrangements, as willbe apparent to one skilled in the relevant arts based on the disclosureand teachings provided herein. For example, the elements ofvariable-length FIR filter 500 can be implemented in hardware, software,or combinations thereof. Variable-length FIR filter 500 can be used toimplement variable-length FIR filter 302 of FIG. 3.

Referring to FIG. 5, variable-length FIR filter 500 includes Nfixed-length FIR filters 502A-N and an output module 504. Fixed-lengthFIR filters 502 can be implemented as conventional FIR filters.Fixed-length FIR filters 502 can have the same lengths or differentlengths.

Fixed-length FIR filter 502A receives an input signal 508, and providesa filtered signal 506A based on input signal input signal 508. Each ofthe remaining fixed-length FIR filters 502B-N receives the filteredsignal 506 output by the previous fixed-length FIR filter 502. Outputmodule 504 provides one of filtered signals 506B-N as an output signal510 in accordance with a control signal 514. Control signal 514 can beprovided by a controller such as controller 304 of FIG. 3.

Control signal 514 changes the length of variable-length FIR filter 500through selection of one of filtered signals 506 to be provided asoutput signal 510. For example, consider a case where N-2, fixed-lengthFIR filter 502A has a length of 2, and fixed-length FIR filter 502N hasa length of 3. In this example, output module 504 can set the length ofvariable-length FIR filter 500 to 2 or 5 by providing filtered signal506A or 506N, respectively, as output signal 510.

FIG. 6 shows a variable-length FIR filter 600 including a plurality offixed-length FIR filters connected in parallel according to anembodiment of the present invention. Although in the describedembodiments, the elements of variable-length FIR filter 600 arepresented in one arrangement, other embodiments may feature otherarrangements, as will be apparent to one skilled in the relevant artsbased on the disclosure and teachings provided herein. For example, theelements of variable-length FIR filter 600 can be implemented inhardware, software, or combinations thereof. Variable-length FIR filter600 can be used to implement variable-length FIR filter 302 of FIG. 3.

Referring to FIG. 6, variable-length FIR filter 600 includes Nfixed-length FIR filters 602A-N and an output module 604. Fixed-lengthFIR filters 602 can be implemented as conventional FIR filters. Eachfixed-length FIR filter 602 has a different length.

Each fixed-length FIR filter 602A-N receives an input signal 608, andprovides a respective filtered signal 606A-N based on input signal inputsignal 608. Output module 604 provides one of filtered signals 606B-N asan output signal 610 in accordance with a control signal 614. Controlsignal 614 can be provided by a controller such as controller 304 ofFIG. 3.

Control signal 614 changes the length of variable-length FIR filter 600through selection of one of filtered signals 606 to be provided asoutput signal 610. For example, consider a case where N=2, fixed-lengthFIR filter 602A has a length of 2, and fixed-length FIR filter 602N hasa length of 4. In this example, output module 604 can set the length ofvariable-length FIR filter 600 to 2 or 4 by providing filtered signal606A or 606N, respectively, as output signal 610.

Class-D amplifier 500 can be implemented in a portable device such as amobile telephone and the like. For example, FIG. 7 shows a mobiletelephone 700 including class-D amplifier 500 of FIG. 5 according to oneembodiment. Although in the described embodiments, the elements ofmobile telephone 700 are presented in one arrangement, other embodimentsmay feature other arrangements, as will be apparent to one skilled inthe relevant arts based on the disclosure and teachings provided herein.For example, the elements of mobile telephone 700 can be implemented inhardware, software, or combinations thereof.

Referring to FIG. 7, mobile telephone 700 includes class-D amplifier500, an antenna 702, a front end 706, a memory 712, a media player 714,an audio switch 718, a speaker 720, and a keypad 722. Of course, mobiletelephone 700 can include other elements such as a microphone, adisplay, and the like, but for clarity, these elements are not shown inFIG. 7.

FIG. 8 shows a process 800 for mobile telephone 700 of FIG. 7 accordingto an embodiment of the present invention. Although in the describedembodiments, the elements of process 800 are presented in onearrangement, other embodiments may feature other arrangements, as willbe apparent to one skilled in the relevant arts based on the disclosureand teachings provided herein. For example, in various embodiments, someor all of the steps of process 800 can be executed in a different order,concurrently, and the like.

Referring to FIG. 8, antenna 702 receives a wireless signal 704representing a voice audio signal 708 (step 802). Front end 706 recoversvoice audio signal 708 from wireless signal 704 (step 804). Memory 712stores one or more music files. Media player 714 plays the music filesas a music audio signal 716 (step 806). Audio switch 718 provides eithervoice signal 708 or music signal 716 to amplifier 500 (step 808). Switch718 can operate according to keypad signals 724 generated by keypad 722.

Amplifier 500 amplifies the signal provided by audio switch 718 (step810). Referring again to FIG. 5, controller 526 selects the length ofvariable-length FIR filter 502. Controller 526 can select the filterlength based on keypad signals 724, by detecting the bandwidth of theaudio signal, and the like. When amplifier 500 includes other multimodemodules, controller 526 can also select the operating modes of themultimode modules as well. Referring again to FIG. 8, amplifier 500provides the amplified audio signal to speaker 720 (step 812).

Embodiments of the invention can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. Apparatus of the invention can be implemented in acomputer program product tangibly embodied in a machine-readable storagedevice for execution by a programmable processor; and method steps ofthe invention can be performed by a programmable processor executing aprogram of instructions to perform functions of the invention byoperating on input data and generating output. The invention can beimplemented advantageously in one or more computer programs that areexecutable on a programmable system including at least one programmableprocessor coupled to receive data and instructions from, and to transmitdata and instructions to, a data storage system, at least one inputdevice, and at least one output device. Each computer program can beimplemented in a high-level procedural or object-oriented programminglanguage, or in assembly or machine language if desired; and in anycase, the language can be a compiled or interpreted language. Suitableprocessors include, by way of example, both general and special purposemicroprocessors. Generally, a processor will receive instructions anddata from a read-only memory and/or a random access memory. Generally, acomputer will include one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM disks. Any of the foregoing canbe supplemented by, or incorporated in, ASICs (application-specificintegrated circuits).

A number of implementations of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other implementations are within the scope of the followingclaims.

1. A multimode audio amplifier comprising: a mode controller adapted toprovide a control signal; and at least one multimode module, whereineach of the multimode modules has a plurality of operating modes,wherein the operating modes are selected in accordance with the controlsignal, wherein changing the operating modes results in a measurablechange in at least one characteristic of the multimode audio amplifier;wherein the characteristics of the multimode audio amplifier consist ofsignal to noise ratio (SNR); total harmonic distortion and noise(THD+N); input to output delay; power consumption; and efficiency. 2.The amplifier of claim 1, wherein the at least one multimode moduleincludes at least one of: an equalizer; a sampling module; a noiseshaper; a pulse width modulator; and an analog output module.
 3. Aportable device comprising the amplifier of claim
 1. 4. A mobiletelephone comprising the amplifier of claim
 1. 5. The amplifier of claim1, further comprising: a variable-length finite impulse response (FIR)filter adapted to provide an output signal based on an input signal,wherein a length of the variable-length FIR filter is selected inaccordance with the control signal, wherein the length of thevariable-length FIR filter represents at least one of an order of thevariable-length FIR filter, and a number of laps of the variable-lengthFIR filter.
 6. A multimode audio amplifier comprising: means forproviding a control signal; and at least one multimode module means foroperating in a plurality of modes, wherein each of the module means hasa plurality of the modes, wherein the modes are selected in accordancewith the control signal, wherein changing the modes results in ameasurable change in at least one characteristic of the multimode audioamplifier; wherein the characteristics of the multimode audio amplifierconsist of signal to noise ratio (SNR); total harmonic distortion andnoise (TI ID-N); input to output delay; power consumption; andefficiency.
 7. The amplifier of claim 6, wherein the at least onemultimode module means includes at least one of: an equalizer; asampling module; a noise shaper; a pulse width modulator; and an analogoutput module.
 8. A portable device comprising the amplifier of claim 6.9. A mobile telephone comprising the amplifier of claim
 6. 10. Theamplifier of claim 6, further comprising: filter means for providing anOutput signal based on an input signal, wherein a length of the filtermeans is selected in accordance with the control signal, wherein thelength of the filter means represents at least one of an order of thefilter means, and a number of taps of the filter means.
 11. An apparatuscomprising: a filter controller adapted to provide a control signal; anda variable-length finite impulse response (FIR) filter adapted toprovide an output signal based on an input signal, wherein a length ofthe variable-length FIR filter is selected in accordance with thecontrol signal, wherein the length of the variable-length FIR filterrepresents at least one of an order of the variable-length FIR filter,and a number of taps of the variable-length FIR filter.
 12. Theapparatus of claim 11, wherein the variable-length FIR filter comprises:a plurality of fixed-length FIR filters, wherein each of thefixed-length FIR filters is adapted to provide a respective filteredsignal based on the input signal, and further wherein each of thefixed-length FIR filters has a different length; and an output moduleadapted to provide one of the filtered signals as the output signal inaccordance with the control signal.
 13. The apparatus of claim 11,wherein the variable-length FIR filter comprises: a first fixed-lengthFIR filter adapted to provide a first filtered signal based on the inputsignal; a second fixed-length FIR filter adapted to provide a secondfiltered signal based on the first filtered signal; and an output moduleadapted to provide one of the first and second filtered signals as theoutput signal in accordance with the control signal.
 14. The apparatusof claim 11: wherein the filter controller provides the control signalbased on at least one of a characteristic of the input signal, and abattery level of a battery providing power to the variable-length FIRfilter.
 15. The apparatus of claim 14, wherein the characteristic of theinput signal comprises at least one of: a type of the input signal; anda bandwidth of the input signal.
 16. The apparatus of claim 15, whereinthe type of the input signal comprises at least one of: voice; andmusic.
 17. An amplifier comprising the apparatus of claim
 11. 18. Theamplifier of claim 17, further comprising: at least one multimodemodule, wherein each of the multimode modules has a plurality ofoperating modes, and wherein the operating modes are selected inaccordance with the control signal.
 19. The amplifier of claim 18,wherein the at least one multimode module includes at least one of: anequalizer; a sampling module; a noise shaper; a pulse width modulator;and an analog output module.
 20. A portable device comprising theamplifier of claim
 17. 21. A mobile telephone comprising the amplifierof claim
 17. 22. An apparatus comprising: filter controller means forproviding a control signal; and filter means for providing an outputsignal based on an input signal, wherein a length of the filter means isselected in accordance with the control signal, wherein the length ofthe filter means represents at least one of an order of the filtermeans, and a number of taps of the filter means.
 23. The apparatus ofclaim 22, wherein the filter means comprises: a plurality of filtersmeans for providing a respective filtered signal based on the inputsignal, wherein each of the filter means has a different length; andoutput means for providing one of the filtered signals as the outputsignal in accordance with the control signal.
 24. The apparatus or claim22, wherein the filter means comprises: first filter means for providinga first filtered signal based on the input signal; second filter meansfor providing a second filtered signal based on the first filteredsignal; and output means for providing one of the first and secondfiltered signals as the output signal in accordance with the controlsignal.
 25. The apparatus of claim 22: wherein the filter controllermeans provides the control signal based on at least one of acharacteristic of the input signal, and a battery level of a batteryproviding power to the filter means.
 26. The apparatus of claim 25,wherein the characteristic of the input signal comprises at least oneof: a type of the input signal; and a bandwidth of the input signal. 27.The apparatus of claim 26, wherein the type of the input signalcomprises at least one of: voice; and music.
 28. An amplifier comprisingthe apparatus of claim
 22. 29. The amplifier of claim 28, furthercomprising: at least one multimode module means for operating in aplurality of modes, wherein each of the module means has a plurality ofoperating modes, wherein the operating modes are selected in accordancewith the control signal, wherein changing the operating modes results ina measurable change in at least one characteristic of the multimodeaudio amplifier.
 30. The amplifier of claim 29, wherein the at least onemultimode module means includes at least one of: means for equalizing;means for sampling; means for shaping noise; means for pulse widthmodulating; and means for analog outputting.
 31. A portable devicecomprising the amplifier of claim
 28. 32. A mobile telephone comprisingthe amplifier of claim 28.